USOO5858066A United States Patent (19) 11 Patent Number: 5,858,066 O'Brien et al. (45) Date of Patent: Jan. 12, 1999

54 PROCESS FOR SEPARATING AND 5,196,616 3/1993 Lee et al...... 95/48 X RECOVERING FILUOROCARBONS AND HCI 5,456.841 10/1995 Lee ...... 95/45 X FROM GASEOUS MIXTURES THEREOF FOREIGN PATENT DOCUMENTS 75 Inventors: William G. O'Brien, Newark, Del.: Barry A. Mahler, Glen Mills, Pa. 59-189926 10/1984 Japan ...... 95/48 61-187918 8/1986 Japan. 73 Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del. Primary Examiner Robert Spitzer 21 Appl. No.: 861,140 57 ABSTRACT 22 Filed: May 21, 1997 An improved process is disclosed for Separating and recov Related U.S. Application Data ering a fluorocarbon and hydrogen chloride (HCl) from a gaseous fluorocarbon/HCl mixture, wherein the fluorocar 63 Continuation-in-partabandoned. of Ser. No. 532,204, Sep. 22, 1995, bon and HCl are difficult to separate by conventional means 6 because of the presence or potential formation of an azeo 51) Int. Cl...... B01D 53/22 trope or azeotrope-like composition in the mixture, Such 52 U.S. Cl...... 95/48; 95/45 process comprising using a Semi-permeable membrane unit 58 Field of Search ...... 95/43, 45, 48 to form a fluorocarbon-depleted Stream and a fluorocarbon 56) References Cited enriched Stream which may then be further processed indi vidually by distillation. U.S. PATENT DOCUMENTS 4.941,893 7/1990 Hsieh et al...... 55/16 12 Claims, 1 Drawing Sheet

AZEOTROPE RECYCLE

AZEOTROPE RECYCLE 28 24

RESIDUAL

18 10

12 FLUOROCARBON 8, HC1. FEED

-114

16

30 PERMEATE HC FLUOROCARBON U.S. Patent 5,858,066

5,858,066 1 2 PROCESS FOR SEPARATING AND may be present which are difficult to Separate using con RECOVERING FILUOROCARBONS AND HCI ventional distillation. FROM GASEOUS MIXTURES THEREOF A method to Solve one particular Such problem is dis closed in U.S. Pat. No. 5,718,807 the entire disclosure of CROSS REFERENCE TO RELATED APPLICATION 5 which is hereby incorporated herein by reference. This This application is a continuation-in-part of application application discloses a method to Solve the Separation prob Ser. No. 08/532,204 filed on Sep. 22, 1995, now abandoned. lems associated with conventional hexafluoroethane manu facturing methods by providing an azeotropic distillation FIELD OF THE INVENTION method for purifying the hexafluoroethane by distilling it in The present invention relates to an improved proceSS for the presence of anhydrous HCl, usually, in the presence of Separating and recovering a fluorocarbon and hydrogen an amount of HCl that is sufficient to form an azeotrope with chloride (HCl) from a gaseous fluorocarbon/HCl mixture, all of the hexafluoroethane. In another aspect of the cited wherein because of the presence or potential formation of an invention, certain other fluorocarbon impurities may also be azeotrope or azeotrope-like composition, it is impractical to Separated from hexafluoroethane in a similar manner by Separate the mixture by conventional distillation. More 15 Virtue of their azeotrope or azeotrope-like compositions basically, the present invention relates to Separating a gas which are formed with anhydrous HCl. eous fluorocarbon/HCl mixture by use of a semi-permeable In Still another aspect of the cited invention, it provides a membrane unit into a fluorocarbon-depleted Stream and a process for breaking the HCl/hexafluoroethane azeotrope fluorocarbon-enriched Stream which Streams may then be into its individual components by liquefying and cooling the further processed individually by repeated contact with the recovered azeotrope, and allowing the cooled composition Semi-permeable membrane or by distillation. to Separate into HCl-rich and hexafluoroethane-rich layers within a decanter. The latter layer may then be decanted and DESCRIPTION OF THE RELATED ART purified by, for example, azeotropic distillation, thereby yielding Substantially pure hexafluoroethane along with a It is well known that fluorocarbons (FCs) of commercial 25 Separate Stream of the hexafluoroethane/HCl azeotrope. interest are typically manufactured by processes involving The HCl-rich layer may also be purified by azeotropic halogen exchange reactions. The term fluorocarbon is used distillation to produce substantially pure anhydrous HCl and herein as a general term to include any halocarbon contain the HC/hexafluoroethane azeotrope. ing fluorine, Such as a chlorofluorocarbon (CFC), hydrogen However, the above liquefaction/decantation proceSS for containing chlorofluorocarbon (HCFC), hydrogen breaking and Separating the HC/hexafluoroethane and/or containing fluorocarbon (HFC), or a perfluorocarbon (PFC). other azeotrope or azeotrope-like compositions into their Generally, an appropriate chlorocarbon or chlorofluorocar respective components has the disadvantage of being bon is reacted with a fluorine-containing compound which energy-intensive. It requires the cooling of the azeotrope or Serves as a fluorine donor to replace at least one of the azeotrope-like compositions to temperatures below about chlorine atoms. In many cases, the fluorine-donating Source 35 -50 to -60 degrees C., followed by heating each decantation is hydrogen fluoride used in the presence of various catalytic layer back to higher temperatures for economical distilla compounds. tion. These distillations only Separate a portion of the Such a proceSS may be illustrated by the preparation of decanted layer into a pure component, the remainder of the hexafluoroethane (C2F6), also known as Perfluorocarbon layer generating an additional large quantity of the Starting 116 (PFC-116) or Fluorocarbon 116 (FC-116). Typically, 40 azeotrope or azeotrope-like composition. This must then be trichlorotrifluoroethane, dichlorotetrafluoroethane or chlo recycledback to or prior to the liquefaction/decantation Step. ropentafluoroethane is the chlorofluorocarbon precursor and hydrogen fluoride is the fluorine donor compound. This is The above liquefaction/decantation process is believed to illustrated in one or more of the following reactions: be specific to the hexafluoroethane process and certain 45 fluorocarbon impurities associated with that process. It is dependent on the mutual Solubilities and relative densities of C.C.F, F3HF satalysis CF, +3 HCI the fluorocarbon and HCl at very low temperatures, and is not necessarily applicable to other fluorocarbon manufac C.C.F, F2HF satalysis CF, + 2 HCI turing processes and their impurities. 50 While the above azeotrope or azeotrope-like composi tions can also be broken and Separated by extracting the HCl CCIFs + HF satalysis CF, + HC with water, this would require Subsequently drying the purified hexafluoroethane or other fluorocarbons or chlorof The catalysts which may be useful in these reactions luorocarbons to remove even traces of water. More include various metal halides or oxides and the reaction can 55 importantly, water extraction would generate an aqueous be carried out either in liquid or vapor phase. When hydro HCl stream which has a much lower market value than gen fluoride is the fluorine donor compound used in the anhydrous HC1. above processes, it is almost always used in excess of the There is a need for a process for Separating azeotropes or Stoichiometric amount required and may be as much as azeotrope-like gaseous compositions of anhydrous HCl with Several times the Stoichiometric amount. In the processes 60 fluorocarbons, and particularly for Separating the azeotrope illustrated by the above equations, the crude reaction Stream of HCl and hexafluoroethane, without the need for energy will contain byproduct HCl and unreacted HF in addition to intensive low temperature liquefaction/decantation Steps or the desired perfluorocarbon, and may as well contain extraction/drying StepS. unreacted, incompletely fluorinated and/or cleavage byprod It has been recognized that anhydrous HCl can be sepa uct chlorofluorocarbons. While the bulk of these impurities 65 rated from certain other gases by Selective permeation can be separated by fractional distillation, others cannot be through a Semi-permeable membrane. For example, U.S. So Separated because azeotropes or azeotrope-like mixtures Pat. No. 4.941,893 (Union Carbide, 7/90) claims a method 5,858,066 3 4 for Separating gaseous Silicon compounds from hydrogen or (a) providing a semi-permeable membrane for separating hydrogen halides by use of a Semipermeable membrane. The fluorocarbon from hydrogen chloride having a feed Side preferred membrane is a polysulfone. and a permeate Side wherein Said Semi-permeable Japanese Patent 61187918 (Asahi Chemical, 8/86) dis membrane is characterized as having a hydrogen chlo close S that gases Such as hydrogen chloride, ride Selectivity for the permeate relative to the non tetrafluoromethane, hexafluoroethane and others can be permeate of greater than 1; dehumidified by contacting them with a fluoro copolymer (b) passing a feed stream of fluorocarbon and hydrogen membrane that has a dry purge gas or depressurized Zone on chloride across the feed side of the Semi-permeable the opposite Side of the membrane. This patent teaches that membrane Such that the hydrogen chloride passes pref hydrogen chloride and hexafluoroethane are equivalent in erentially through the membrane to form a their behavior under the permeation conditions exemplified. fluorocarbon-depleted hydrogen chloride permeate Still other references teach methods of purifying aqueous Stream and a fluorocarbon-enriched residual Stream. acid Solutions by use of Semi-permeable membranes. None According to one aspect of the present invention, if either of the above references teach a process for efficient Separa the permeate Stream or the residual Stream exiting the tion of azeotropes or azeotrope-like gaseous compositions of 15 Semi-permeable membrane means is Sufficiently pure that anhydrous hydrogen chloride and fluorocarbons. Subsequent distillation is not necessary, only the other SUMMARY OF THE INVENTION Stream may be Subjected to distillation. In one preferred embodiment according to the present invention, the The present invention provides an improved proceSS for fluorocarbon-depleted hydrogen chloride permeate Stream is Separating and recovering an organic Stream containing further characterized as having a hydrogen chloride concen fluoro carbons (e.g. chlorofluoro carbons, tration above that characteristic of the azeotrope or hydrochlorofluorocarbons, hydrofluorocarbons, perfluoro azeotrope-like composition involving hydrogen chloride and carbons and compounds containing only fluorine and the fluorocarbon Such that the azeotrope or azeotrope-like carbon) and a hydrogen chloride Stream from gaseous composition is also separated and recovered in the Subse fluorocarbon/hydrogen chloride mixtures, particularly mix 25 quent and optional distillation Step. The fluorocarbon tures wherein because of the presence or potential formation enriched residual Stream may be characterized as having a of an azeotrope or azeotrope-like composition, it is imprac hydrogen chloride concentration below that of the azeotrope tical to Separate the mixture by conventional distillation. The or azeotrope-like composition involving hydrogen chloride improved method according to the present invention and the fluorocarbon Such that the azeotrope or azeotrope involves the Simultaneous use of a gas-phase membrane like composition is also separated and recovered in the Separation System with Subsequent optional conventional Subsequent and optional distillation Step. The azeotrope or distillation Systems, thus producing a hybrid recovery unit. azeotrope-like compositions Separated and recovered in the In particular, but not by way of limitation, this invention Subsequent and optional distillation steps may be recycled to provides a proceSS for the Separation of a difficult-to the inlet Side of the Semi-permeable membrane unit. Separate azeotrope or azeotrope-like gaseous mixture con 35 It is an object of the present invention to provide an Sisting essentially of a fluorocarbon composition and hydro effective and economical process for Separating an azeotrope gen chloride. or azeotrope-like gaseous mixture of anhydrous hydrogen Thus, the present invention provides a proceSS for Sepa chloride and a fluorocarbon composition. It is a further rating and recovering a fluorocarbon phase and a hydrogen object of the present invention to provide a proceSS for chloride phase from a gaseous feed Stream of a mixture of 40 Separating and recovering the components of an azeotrope or fluorocarbons and anhydrous hydrogen chloride wherein the azeotrope-like gaseous mixture of hydrogen chloride and a mixture is characterized as forming at least one azeotrope or fluorocarbon composition which does not create any addi azeotrope-like composition involving at least one fluorocar tional waste product disposal problems. It is a still further bon and hydrogen chloride, comprising the steps of: (a) object of the present invention to provide a separation providing a Semi-permeable membrane means for gas-phase 45 process for an azeotrope or azeotrope-like gaseous mixture Separation of fluorocarbons from hydrogen chloride wherein of hydrogen chloride and a fluorocarbon composition which the Semi-permeable membrane means is characterized as provides the components of Said azeotrope or azeotrope-like having a hydrogen chloride Selectivity for the permeate mixture in essentially pure forms. Fulfillment of these relative to the non-permeate of at least 3; (b) passing the objects and the presence and fulfillment of other objects will gaseous feed Stream of fluorocarbons and hydrogen chloride 50 be apparent upon complete reading of the Specification and acroSS the feed Side of the Semi-permeable membrane Such claims taken in conjunction with the attached drawing. that hydrogen chloride passes preferentially through the membrane to form a fluorocarbon-depleted hydrogen chlo BRIEF DESCRIPTION OF THE DRAWING ride permeate Stream and a fluorocarbon-enriched residual Stream. Subsequently and optionally, the fluorocarbon 55 FIG. 1 represents a Schematic illustration of a typical depleted Stream from Step (b) may be distilled, thus sepa improved proceSS for recovery of organic/hydrogen chloride rating and recovering anhydrous hydrogen chloride, and, the compositions according to one embodiment of the present fluorocarbon-enriched Stream from Step (b) may also be invention. distilled, thus Separating and recovering a fluorocarbon DETAILED DESCRIPTION OF THE organic composition. 60 A process is disclosed for Separating and recovering a INVENTION fluorocarbon composition and a hydrogen chloride compo The feed Stream to be separated according to the Sition from a feed Stream of a mixture of fluorocarbon and improved process of the present invention can be any hydrogen chloride wherein Said mixture is characterized as mixture of at least one fluorocarbon and hydrogen chloride forming at least one azeotrope or azeotrope-like composition 65 that results in a fluorocarbon/HCl admixture that is difficult involving at least one fluorocarbon and hydrogen chloride, to Separate by conventional distillation. Hence, for the comprising the Steps of purposes of the present invention, fluorocarbon refers 5,858,066 S 6 broadly to any chlorofluoro carbon, carbons can result in mixtures which contain Some of these hydrochlorofluoro carbon, hydrofluorocarbon, disclosed fluorocarbon/HCl azeotropes or azeotrope-like perfluorocarbon, compounds which contain only fluorine combinations, or can contain other fluorocarbon/HCl azeo andcarbon (i.e., CFC, HCFC, HFC., PFC and FC trope or azeotrope-like combinations. These mixtures are respectively) or mixtures thereof that form or tend to form particularly amenable to the benefits of the present inven a mixture with HCl that is difficult to separate by conven tion. tional distillation. AS Such, the term fluorocarbon is intended The present invention provides a separation proceSS for to include fluorocarbons that form or tend to form true difficult-to-separate fluorocarbon mixtures which avoids azeotropes with HCl as well as fluorocarbons that form or energy-intensive liquefaction Steps, does not require the tend to form azeotrope-like compositions with HCl. In other addition of any extraneous components to the mixture to be words, the feed Stream according to the present invention Separated, does not alter any of the components of the does not have to be at the azeotrope or azeotrope-like fluorocarbon composition and minimizes or eliminates any concentration range but merely capable of forming a additional waste disposal problems. In essence, in the difficult-to-separate composition during distillation (as present invention, the difficult-to-separate fluorocarbon/HCl explained more fully later). 15 composition is initially treated with a Selected Semi For purposes of the present invention, the term azeotrope permeable polymer membrane which provides two refers to a constant boiling mixture of one or more fluoro compositions, each of which is enriched in one or the other carbons with HCl, which mixture behaves as a single of the components in the original composition (i.e. either the Substance, in that the vapor, produced by partial evaporation organic component or the HCl component). Subsequent and or distillation of the liquid has the same composition as the optional treatment, Such as distillation of the two liquid, i.e. the mixture distills without Substantial composi compositions, can then provide the components of the tional change. Analogously, the term azeotrope-like, for original composition in more purified forms. purposes of this invention, refers generally to any Such The present invention may perhaps be best explained and mixture of one or more fluorocarbons and HCl that exhibits understood by reference to the drawing and by illustrating a Substantially constant composition on boiling (i.e. distills 25 the Separation of an azeotrope or azeotrope-like mixture of with little or no change in composition due to the closeneSS hexafluoroethane and hydrogen chloride (HCl) relative to of the boiling points of the components in the mixture or due the FIGURE as one embodiment. As previously mentioned, to Some other reasons). hexafluoroethane is typically manufactured by the process of The fluorocarbons of particular use in the present inven fluorinating trichlorotrifluoroethane, dichlorotetrafluoroet tion include, by way of example but not limited thereto, hane or chloropentafluoroethane using hydrogen fluoride as aliphatic fluorocarbons of 1 to 3 carbon atoms containing at the fluorine Source. Hydrogen chloride is then a byproduct least one fluorine atom Substituent. Thus, the term fluoro of the reaction. If the azeotropic distillation process previ carb on will include chlorofluoro carbon, ously cited in U.S. Pat. No. 5,718,807 is employed, addi hydrochlorofluorocarbon, hydrofluorocarbon, perfluorocar tional HCl may be added as part of the part of the purifi bon or a fluorocarbon which contains only fluorine and 35 cation process to remove unwanted fluorocarbon impurities. carbon of from 1 to 3 carbon atoms and mixtures of all of In any case, at Some point in the purification Sequence for these. More Specifically, fluorocarbons of particular interest hexafluoroethane, a mixture of hydrogen chloride and include hexafluoroethane, chloropentafluoroethane, hexafluoroethane may result which cannot be separated by dichlorotetrafluoroethane, trichlorotrifluoroethane, conventional distillation because hydrogen chloride and difluoroethane, trifluoroethane, pentafluoroethane, 40 hexafluoroethane form an azeotrope or azeotrope-like mix chlorotrifluorome thane, chloro difluorome thane, ture containing about 36 to 40 mole percent hexafluoroet difluoromethane, and trifluoromethane. In addition, the fluo hane and 64 to about 60 mole percent hydrogen chloride. rocarbons in the present invention may also include unsat Such a mixture, under current practices, is usually treated by urated fluorocarbons Such as tetrafluoroethylene and Scrubbing the HCl from the mixture, resulting in an aqueous hexafluoropropylene. 45 stream of HCl to be sold or disposed of. This usually results In addition to the separation of individual fluorocarbons in the loss of most of the sales value of the hydrogen chloride from their mixtures with HCl, the improved process of the because of a limited market for aqueous HCl. In many cases present invention is particularly useful in Separating and the aqueous HCl must be neutralized and otherwise disposed recovering various mixed fluorocarbons from their mixtures of, resulting in Still greater cost as well as an undesirable with HC1. Frequently commercial production of a fluoro 50 effect on the environment. carbon involves a Sequential fluorination of a starting If the optional liquefaction process disclosed in U.S. Pat. chlorocarbon, resulting in a distribution of reaction products No. 5,718,807 is employed, this specific azeotrope or and intermediates, all of which tend to make the mixture azeotrope-like composition can be broken by liquefaction even more complex and difficult to Separate and makes and decanting. However, this liquefaction proceSS is energy recovery of desired products more difficult by conventional 55 intensive because of the low temperatures (-50 to -60 distillation techniques. Thus various members of the fluo degrees C.) required for liquefaction, the need to reheat to roethane Series are frequently found together along with much higher temperatures for Subsequent distillation Steps, byproduct HCl and other impurities such as unreacted HF and the large amount of azeotrope produced in the distilla and certain halomethanes resulting from haloethane cleav tion StepS which must be recycled. Furthermore, it is a age reactions. 60 Specific proceSS applicable to certain hexafluorethane/HCl As disclosed in previously cited U.S. Pat. No. 5,718,807, compositions and which is not necessarily applicable to certain of these compounds form azeotropes with HCl, other fluorocarbon/HCl azeotrope or azeotrope-like compo making Such mixtures unsuitable for Separation from HCl by Sitions. In contrast and as conceptionally illustrated in the distillation. These mixtures can occur either because of FIGURE, in the present process the above hexafluoroethane/ byproduct HCl or because of HCl added to remove certain 65 HCl composition is typically introduced into a membrane organic impurities as disclosed in the referenced patent separation unit 10 via inlet 12 as the fluorocarbon/HCl feed application. Manufacturing processes for Still other fluoro stream. Within the separation unit 10, the feed stream makes 5,858,066 7 8 contact with Selected Semi-permeable polymer membrane not limited thereto, a Semi-permeable membrane thin layer 14. Because of the preferential permeability of HCl across of film (i.e. the So-called plate and frame unit), a spiral the membrane 14, the Separation unit 10 produces a perme wound membrane, a hollow fiber Semi-permeable mem ate Stream exiting via line 16 wherein the concentration of brane and the like (including combinations of Such devices). HCl is enriched typically about 3 fold or more relative to its For the Semi-permeable membrane to Separate the concentration in the nonpermeate residual Stream. fluorocarbon/HCl mixture into a fluorocarbon-depleted per Simultaneously, a non-permeate residual Stream is continu meate Stream and a fluorocarbon-enriched residual Stream, ously withdrawn via line 18 wherein the HCl concentration there must be a difference or Selectivity in the permeation is proportionately depleted relative to the permeate compo rates for the fluorocarbon and the HCl compositions. For sition. Thus, in the hexafluoroethane/HCl azeotrope purposes of this invention, the necessary preferential per illustration, a typical feed stream to the membrane unit 10 meation rate for the HCl through the membrane relative to would be at about 25 degrees C. and about 200 psig (1480 the permeation rate of the fluorocarbon phase can be Satis fied and/or confirmed by considering the ratio of the HCl KPa, absolute) and would contain about 62 mole percent concentration in the permeate relative to the concentration of HCl. The residual stream exiting outlet 18 would have an HCl in the non-permeate. This ratio, hereinafter referred to HCl concentration reduced to about 11 mole percent, rep 15 as HCl Selectivity, can vary from as little as greater than 1 resenting Substantial one-pass recovery. to more typically 5 or higher and is frequently higher than By taking advantage of the fact that the fluorocarbon 8. Preferably this selectivity should be 5 or greater. (hexafluoroethane, the illustrated embodiment) and HCl AS in any permeation Separation process, the parameters form an azeotrope, more purified fluorocarbon and more usually considered as variables to enhance the Separation purified HCl may be recovered by Subsequent distillation process are the temperature, the pressure differential Steps. Thus, the permeate composition exiting the membrane between the feed side of the permeation membrane and the unit 10 via line 16 may be distilled in column 20. The small permeate Side of the membrane, the residence time of the amount of fluorocarbon/HCl azeotrope being distilled over feed stream on the feed side of the membrane, and the head may be then recycled via line 24 to the feed side of the residence time of the permeate Stream on the permeate Side permeation unit 10 and essentially purified HCl may be 25 of the membrane. To achieve reasonable productivity at a recovered as distillation bottoms via line 26. If the azeotro desireable quality, the polymer membrane which does the pic distillation process of U.S. Pat. No. 5,718,807 is actual Separation may be quite thin, i.e., less than 1 micron. employed for the purification of hexafluoroethane, the HCl Due to Some process requirements and dew point limitations can be recycled in lieu of fresh HCl to the azeotropic for Some fluorocarbons, the Separation unit may be operated distillation System. Similarly, the non-permeate residual over a range of temperatures, e.g., 0 to 75 degrees C. For low composition exiting the membrane unit via line 18 may be cost and to minimize equipment size the inexpensive hollow distilled in column 22. The Small amount of fluorocarbon/ fiber configuration is preferred over the usually more expen HCl azeotrope being distilled overhead may be recycled via sive spiral wound module. Typically hollow fibers provide 10 to 30 times the membrane surface area relative to spiral line 28 to the feed side of the permeation unit 10 and purified wound elements for a given proceSS Volume. To facilitate fluorocarbon may be recovered via line 30 from the distil 35 desorption into the permeate gas phase, the permeate Side of lation bottoms. Of course, both the HCl and fluorocarbon the membrane should operate at lower preSSure relative to may be Subjected to further purification, if desired. Also, if the upstream feed Side. The membrane Structure must be either the permeate or non-permeate Streams can be utilized integrally Strong to withstand the net force associated with without Subsequent distillation, then one of the columns may this pressure differential. For example, a 1 Square foot be eliminated and a single column in combination with the 40 membrane operation with an average upstream pressure of membrane unit may be employed and should be considered 100 psig and downstream permeate preSSure of 10 psig must an equivalent process for the purpose of this invention. withstand a deformation force of over 6 tons. In the instant The Semi-permeable polymer membrane useful in the invention, these parameters are not critical So long as the present invention for the permeation Step of the proceSS may membrane material is not destructively affected and the HCl be any hydrogen chloride-resistant polymeric material 45 Selectivity is not lost. which can be formed into any shape which exhibits the Temperature is not critical and may be any convenient desired Selective permeability as defined later. The Semi temperature, usually from about 0 to 150 degrees C. The permeable polymer membrane, Seals and physical housing primary temperature limitations are the temperature should of the Separation unit should be chemically resistant to long be below any temperature at which the membrane is affected term HCl exposure especially when water is present at trace 50 adversely and above the dew point of the fluorocarbon. levels. In addition, the polymer should typically have a Conveniently, the temperature range will be between about number of polar groups as part of the repeating chain to 0 and about 75 degrees C. facilitate initial sorption of the highly polar HCl over the less The pressure differential between the feed side of the membrane and the permeate Side is not critical but is polar fluorocarbon. The polymer should typically be fairly preferentially at least about one-tenth (0.1) atmosphere. The dense, glassy (Tg greater than 50 degrees C.) to allow a 55 process may be operated at a lower pressure differential but reasonable diffusional transport rate of the Small HCl species the Separation process will be slower. The pressure differ yet impede the relatively large bulky fluorocarbon. Polyim ential can be the result of higher pressure on the feed Side of ide membranes already in commercial use for conventional the Semi-permeable membrane or the result of reduced (e.g. oxygen/nitrogen Separations) gas Separation processes, preSSure on the permeate Side of the membrane or both. Such as 1,3-isobenzofurandione, 5,5'-carbonylbis-, polymer 60 The following examples are presented to further illustrate with 1 (or 3)-(4-aminophenyl)-2,3-dihydro-1,3,3(or 1,1,3)- Specific embodiments of the invention. All references to trimethyl-1H-inden-5-amine (manufactured by Ciba-Geigy percentages of composition are mole percent unless other as Matrimid(R) 5218), are preferred because of convenience wise indicated. and low cost. The Semi-permeable membrane unit (the permeator) use 65 EXAMPLE 1. ful in the present invention can be generally any Such device A 690 gram mixture of 477 grams of PFC-116 and 213 as is well known in the art, including by way of example, but grams of anhydrous HCl was placed in a 2-liter preSSure 5,858,066 9 10 cylinder at 750 psig (5276 KPa, absolute) cylinder pressure. In the above trial, the overall HCl selectivity (defined as This corresponds to about 37.2 mole % PFC-116 and 62.8 the ratio of HCl in the permeate to that in the non-permeate) mole % HCl, the azeotrope composition. The cylinder was was 14.6. However, the inadequate time at Steady State connected to a flow measuring device and then to the inlet conditions indicated a need for additional trials to establish Side of a permeation Separator with a commercial polyimide Steady State operation results. membrane in the form of a hollow fiber. The membrane used was Ciba-Geigy's Matrimid(R) 5218 polyimide skin covering EXAMPLE 2 a bulk porous fiber wall made of General Electric's Ultem(R) A 695 gram mixture of 477 grams of PFC-116 and 218 1000 (a high molecular weight polymer). The permeate gas grams of anhydrous HCl was placed in a 2-liter preSSure was fed to a flowmeter, then to a Scrubbing tank containing cylinder at 750 psig (5276 KPa, absolute) cylinder pressure. 2.5% NaOH, and then to a flowmeter at 0 psig (101 KPa, This corresponds to about 36.7 mole % PFC-116 and absolute). The non-permeate gas was fed to a flowmeter and 63.3mole % HCl, near the azeotrope composition. The same then to a cylinder immersed in liquid nitrogen at -195 apparatus and membrane was used as in Example 1. degrees C. and 0 psig (101 KPa, absolute). The cylinder pressure was reduced and regulated to a The cylinder preSSure was reduced and regulated to a 15 steady 90 psig (122 KPa, absolute) feed inlet pressure with steady 120 psig (929 KPa, absolute) as feed inlet pressure the temperature regulated to 25 degrees C. A needle valve and the temperature was regulated to 25degrees C. A needle was used to control the exit pressure for the non-permeate Valve was used to control the exit preSSure for the non permeate gas at 105 psig (826 KPa, absolute). A nominal 6 gas at 75psig (619 KPa, absolute). A nominal 6 psig (143 psig (142 KPa, absolute) permeate back pressure was cre KPa, absolute) permeate back pressure was created by the ated by glass frit used to Sparge the permeate gas into the glass frit used to Sparge the permeate gas into the base of the base of the scrubbing tank. The feed cylinder weight loss Scrubbing tank. Measurements of flows and compositions was continuously measured during the course of the experi were made as in Example 1. ment. The experiment was stopped shortly after the cylinder Under these conditions, a steady State operation was pressure dropped below the desired 120 psig (929 KPa, 25 achieved in about 50 to 60 minutes and continued for a total absolute), a period of about 70minutes. It was noted that the operating time of about 110 minutes. Recovery of HCl was preSSure in the liquid nitrogen receiver rose during the 99.4% complete, and the recovery of PFC-116 was 96.3% course of the experiment, presumably caused by a tempera complete. ture rise due to the insulating effect of the progressive Overall separation results are shown in Table 2 below, build-up of frozen PFC-116 on the receiver walls. with results expressed in mole %; The Scrubbing tank was completely effective in removing HCl, as shown by repeated tests with wet litmus paper. The TABLE 2 PFC-116 removed by the scrubbing tank was negligible due to its extremely low solubility in dilute room temperature Separation of PFC-116/HCl at 90 psig caustic solution. While the flow into the scrubbing tank 35 Component Feed Permeate Non-permeate began almost immediately at about 2.5 literS/minute, it took PFC-116 36.6 14.7 91.3 over 13 minutes for a measurable flow of gas (about 0.02 HCI 63.4 85.3 8.7 liters/minute) to appear in the outlet from the Scrubbing tank. This indicates that HCl permeated through the membrane quickly, while there was a Substantial lag in the permeation 40 Overall HCl selectivity was about 9.8. While this ratio of PFC-116, believed to be initial evidence of a large was lower than that in Example 1, it is a much better difference in diffusivity rates between the HCl and the example of Steady State performance. PFC-116. As the permeation proceeded, the percent of PFC-116 in the permeate gradually increased, indicating that EXAMPLE 3 the HCl may slightly plasticize the polymer skin layer, 45 A 678 gram mixture of 476 grams of PFC-116 and 202 causing it to Swell and increase the diffusivity of the PFC grams of anhydrous HCl was placed in a 2-liter preSSure 116 relative to the HC1. In this trial, steady state conditions cylinder at 750 psig (5276 KPa, absolute) cylinder pressure. were apparently reached just as the feed materials in the This corresponds to about 38.4 mole % PFC-116 and 61.6 preSSure cylinder were being exhausted. Overall material mole % HCl, near the azeotrope composition. The same balances were based on the weight loSS in the preSSure 50 apparatus and membrane was used as in Example 1. cylinder, weight gain in the liquid nitrogen receiver, caustic The cylinder pressure was reduced and regulated to a consumption in the Scrubbing liquid, and caustic Scrubbing steady 60 psig (515 KPa, absolute) feed inlet pressure with of the non-permeate. These indicated that the recovery of the temperature regulated to 25 degrees C. A needle valve HCl was 99.8% complete, and the recovery of PFC-116 was 55 was used to control the exit pressure for the non-permeate 99.6% complete. gas at 45 psig (412 KPa, absolute). A nominal 6 psig (143 Overall separation results are shown in Table 1 below, KPa, absolute) permeate back pressure was created by the with results expressed in mole %: glass frit used to Sparge the permeate gas into the base of the Scrubbing tank. Measurements of flows and compositions TABLE 1. 60 were made as in Example 1. Under these conditions, a steady State operation was Separation of PFC-116/HCl at 120 psig (929 KPa. absolute achieved in about 10 minutes and continued for a total Component Feed Permeate Non-permeate operating time of about 160 minutes. Recovery of HCl was PFC-116 37.2 9.4 93.8 98.9% complete, and the recovery of PFC-116 was 95.3% HCI 62.8 90.6 6.2 65 complete. Overall separation results are shown in Table 3 below, with results expressed in mole %: 5,858,066 11 12 (a) providing a semi-permeable membrane for separating TABLE 3 Said fluorocarbon from Said hydrogen chloride having a feed Side and a permeate Side wherein Said Semi Separation of PFC-116/HCl at 60 psig permeable membrane is characterized as having a hydrogen chloride Selectivity for the permeate relative Component Feed Permeate Non-permeate to the non-permeate of greater than 1, PFC-116 38.4 13.4 88.9 (b) passing a feed stream of Said mixture of fluorocarbon HCI 61.6 86.6 11.1 and hydrogen chloride across the feed Side of the Semi-permeable membrane Such that the hydrogen Overall HCl selectivity was about 7.8. Again, this ratio chloride passes preferentially through the membrane to was lower than that in Example 1 but a better example of form a fluorocarbon-depleted hydrogen chloride per Steady State performance. meate Stream and a fluorocarbon-enriched residual Stream. The above results show that an azeotrope of PFC-116 and 2. The process of claim 1 wherein said fluorocarbon anhydrous HCl can be separated by a polyimide membrane depleted hydrogen chloride Stream is Subsequently distilled into an HCl-rich permeate and a PFC-116-rich non-permeate 15 or further purified with a semi-permeable membrane to form at room temperature. The resulting compositions are very a more purified hydrogen chloride composition. different than the azeotrope composition, making Subse 3. The process of claims 1 or 2 wherein said fluorocarbon quent separations into pure PFC116 and HCl by distillation enriched residual stream is distilled or further purified with easy to carry out by one skilled in the art, and yielding only a Semi-permeable membrane to form a more purified fluo a relatively Small fraction of azeotrope which requires rocarbon composition. recycle. 4. The process of claims 3 wherein said fluorocarbon For this Same Separation, the previously described depleted HCl Stream is further characterized as having a liquefaction/decantation proceSS had a much lower HCl hydrogen chloride concentration above that of Said azeo selectivity. If we define its HCl selectivity for comparison trope or azeotrope-like composition contained in Said feed purposes as the ratio of the HCl content of the upper and 25 Stream. lower decanted layers, this selectivity was only 1.8 at -50 5. The process of claim 3 wherein said fluorocarbon degrees C. Even when the liquefaction/decantation tempera enriched residual Stream is further characterized as having a ture was reduced to -60 degrees C., the HCl selectivity was fluorocarbon concentration above that of Said azeotrope or improved only to 3.2. azeotrope-like composition contained in Said feed Stream. AS a result the decanted layers are much closer in com 6. The process of claim 3 wherein said semi-permeable position to the Starting azeotrope composition than the membrane is a polyimide polymer. present inventive membrane process. This means that the 7. The process of claim3 wherein said step (b) is operated liquefaction/decantation process will require a much higher at a temperature of 0 to 150 degrees C. recycle of azeotropic material after any Subsequent distilla 8. The process of claim3 wherein step said (b) is operated tion Step than the present inventive process. This higher 35 with a pressure differential between said feed side of the recycle rate will require larger, more expensive distillation membrane and the permeate Side of the membrane of greater columns, utilizing Still more energy for boilup and reflux in than 0.1 atmospheres. addition to the high energy requirements of the low tem 9. A process for Separating and recovering a fluorocarbon perature liquefaction Step. composition and a hydrogen chloride composition from a 40 feed Stream of a mixture of fluorocarbon and hydrogen EXAMPLE 4 chloride wherein Said mixture is characterized as forming at Using the same apparatus and hollow fiber System least one azeotrope or azeotrope-like composition involving described in EXAMPLE 1, an azeotrope mixture of anhy at least one fluorocarbon and hydrogen chloride, comprising drous HCl (74.3 m%) and tetrafluoroethylene (TFE) was fed the Steps of to the hollow fibers at a rate of 4.8 g/minute at a nominal 45 (a) providing a semi-permeable membrane for separating preSSure of 60 psig with an axial pressure of 50 psig and a Said fluorocarbon from Said hydrogen chloride having permeate pressure of ~0 pSig. The temperature of the hollow a feed Side and a permeate Side wherein Said Semi fibers was allowed to run to 22 degrees C. A steady State was permeable membrane is characterized as having a reached in 40 to 45 minutes. Based on a volumetric feed rate hydrogen chloride Selectivity for the permeate relative of approximately 0.4lt/min (60 psig) and total fiber volume 50 to the non-permeate of greater than 1, of 1.4 cm, the average residence was ~0.2 second. The passing a feed Stream of Said mixture of fluorocarbon and permeate vapor was 85.1 m % HCl, and the non-permeate hydrogen chloride across the feed side of the Semi vapor was 34.0 m 9% HC1. permeable membrane Such that the hydrogen chloride The above results for the inventive membrane separation passes preferentially through the membrane to form a proceSS can be readily optimized by one skilled in the art by 55 fluorocarbon-depleted hydrogen chloride permeate utilizing other membranes, Separation pressures, tempera Stream and a fluorocarbon-enriched residual Stream; tures and hold times. By Simple experimentation not wherein (i) said fluorocarbon-depleted hydrogen chlo amounting to invention this inventive process may also be ride Stream has a hydrogen chloride concentration extended to other fluorocarbon/HCl above that of Said azeotrope or azeotrope-like compo I claim: 60 Sition contained in said feed stream; (ii) said 1. A proceSS for Separating and recovering a fluorocarbon fluorocarbon-enriched residual Stream has a fluorocar composition and a hydrogen chloride composition from a bon concentration above that of Said azeotrope or feed Stream of a mixture of fluorocarbon and hydrogen azeotrope-like composition contained in Said feed chloride wherein Said mixture is characterized as forming at Stream, and (iii) said fluorocarbon is selected from the least one azeotrope or azeotrope-like composition involving 65 group consisting of C1 to C3 chlorofluorocarbons, at least one fluorocarbon and hydrogen chloride, comprising hydrochlorofluorocarbons, hydrofluorocarbons, and the Steps of compounds containing only carbon and fluorine. 5,858,066 13 14 10. The process of claim 9 wherein said fluorocarbon is 12. The process of claim 9 wherein said semipermeable hexafluoroethane. membrane is a polyimide polymer. 11. The process of claim 9 wherein said fluorocarbon is tetrafluoroethylene. k . . . .